Background: The Office of Primary Care (OPC) is charged with overseeing primary care in the Department of Veterans Affairs (VA). In 2010, VA primary care moved to a medical home model called the Patient Aligned Care Team (PACT). Over 5.7 million Veterans are assigned, or “empaneled”, to a primary care provider and team. Current VA panel sizes are based on historic means and there are concerns that these metrics should be updated given high rates of burnout among primary care providers. However, the evidence base is thin, and a recent a recent HSR&D Evidence Synthesis Program (ESP) report calls for greater evidence to manage the primary care work force of 7,995 primary care physicians and providers (PCP). Significance/Impact: This study will assist the VA with managing its primary care workforce to balance the needs for efficiency and the wellness of the workforce. The novel methods in this study will set the stage for future randomized program evaluations that can test ways to improve efficiency and outcomes for providers and patients. Innovation: The goal of the proposed study is to provide foundational evidence on primary care panel size by adapting and extending a recently developed methodology to assess the workload of primary care patients. The results of this study have a high probability of immediate impact in the VA by informing primary care work force management, in addition to providing evidence that longitudinal patient histories can be used to estimate time and workload for primary care panels. Specific Aims: Aim 1: To describe weekly demand, weekly capacity, and weekly overflow (i.e., demand > capacity) for every PCP and how these parameters vary by PCP, by team, by clinic and by health care system. Aim 2: To determine whether system-level funding is associated with PCP overflow. We will examine the association between the system funding and PCP overflow. Aim 3: To identify which patient events are leading to overflow. This aim examines random variation in weekly patient flow to determine whether random “shocks” in patient events are leading to overflow. Aim 4: To examine overflow in relation to workforce health, measured by provider burnout and turnover. Methodology: The proposed study extends a recently developed methodology to assess the workload of primary care patients and use this workload to develop time estimates for caring for populations of patients. This approach, recently published by Rossi et al. (2018), uses longitudinal data to enumerate patient-related events, or transactions, including both face to face visits and non-face to face care. These transactions are then combined with time estimates per transaction to determine the time it would take to care for a panel of patients. The method provides information on the flow of patients and the demand on primary care providers, and allows for calculation of overflow, where demand would exceed capacity to supply services. We have piloted this method in one health care syste...